1. Field of the Invention
This invention relates to an adjustable stabilizer bar for a vehicle.
2. Description of Related Art
Torsional stabilizer bars have proven useful in vehicles for many years. Such stabilizer bars commonly employ a transverse torsion bar segment pivotally attached to the vehicle chassis and leading or trailing longitudinal segements attached to a control arm or wheel carrier. Examples of stabilizer bars having this particular configuration are shown in U.S. Pat. Nos. 2,660,449, 3,181,885, 3,733,087, 4,066,278, and 4,143,887. These stabilizers act in a manner such that when a pair of left and right wheels differ in level from each other due to a cornering maneuver. the vehicle body will be prevented from excessive rolling or leaning to either side by the torsional resistance produced in the stabilizer bar.
In response to the driving public's demand for more "sporty" cornering capability, automotive designers have increased the diameters of conventional stabilizer bars. Although this modification beneficially increases roll stiffness, it also degrades ride quality in many cases. This results because the stabilizer couples the wheels together. For example, when one wheel strikes a raised obstruction in the roadway during straight running, the body will tend to roll more when a stronger or stiffer stabilizer is used than when a bar of lesser torsional stiffness is fitted.
Designers have sought to enhance the function of stabilizer bars in a variety of ways. U.S. Pat. No. 4,206,935 discloses a non-adjustable stabilizer bar with two halves which may be selectively coupled or entirely decoupled by means of a clutch mechanism. This stabilizer cannot produce varied degrees of stabilization. U.S. Pat. No. 3,197,233 discloses an active stabilizer system in which a bifurcated stabilizer bar is loaded torsionally by a hydraulic motor joining the two furcations. This system is limited because it requires an external pump driven by the vehicle's engine. It is further limited because torsional bias can be applied only when the vehicle is in a leaning situation; application of the bias when the vehicle is operating in a straight-ahead mode will cause the body to roll to one side. This necessarily limits the flexibility of the control strategy of the device.
U.S. Pat. No. 3,292,918 discloses a variable rate stabilizing assembly comprising a transversely mounted multipiece leaf spring coupled at its ends to the swing axle of an independent rear suspension. The roll stiffness produced by this system is not adjustable while the vehicle is in motion.
U.S. Pat. No. 3,490,786 discloses a variable action anti-roll mechanism in which a longitudinal segment of a stabilizer bar is selectively coupled to a transversely running torsional reaction segment. The stabilization capability of this system is limited by the stiffness of the simple transverse torsional reaction segment.
U.S. Pat. No. 3,589,700 discloses a flexibility corrector for a vehicle suspension system in which a resilient member mounted to a stabilizer bar alters the suspension spring rate when the wheels of the suspension move into jounce or rebound positions. U.S. Pat. No. 3,337,236 discloses a suspension having variable rate torsion bar springs but no stabilizer feature. Finally, German Auslegeschrift No. 1,160,313 discloses an adjustable torsion bar suspension including ride height control.
It is an object of the present invention to provide an adjustable stabilizer bar which does not require an engine driven pump and which permits either the driver or an automatic system to select the desired stiffness of the torsional reaction segment of the stabilizer bar. This allows a less powerful stabilizer bar to be employed in the normal course of events while permitting a stiffer bar to be used according to the driver's wishes or the dictates of the road.